The present invention relates to blood pressure measuring apparatus in general and in particular to a fully automatic, non-invasive, digitally-controlled apparatus with digital registers and LED's for providing a readout of systolic and diastolic blood pressure levels.
Typically, the systolic blood pressure is defined as that pressure in the vascular system which exists when the heart is active -- i.e., pumping. It is determined as corresponding to the pressure in a cuff required to effect approximately total occlusion of the brachial artery. The diastolic pressure, on the other hand, is defined as that pressure in the vascular system existing when the artery returns to its non-occluded shape. It is determined as corresponding to the pressure in a cuff when an artery becomes approximately fully patent. Whether an artery is occluded or patent is determined by the sounds or lack of sounds created by the blood coursing through the artery. These sounds, commonly called Korotkoff sounds or pulses, are measurable as the artery is partially occluded.
In the course of taking a blood pressure measurement, the Korotkoff sounds are found to vary in amplitude and frequency. Moreover, the amplitude and frequency of the sounds may, and usually do, vary from individual to individual. Also, as is found when using a stethoscope, it is quite difficult to detect quantitatively a change in the sound intensity -- i.e., amplitude. Noise is frequently prominent and partly to blame for this difficulty.
For these reasons, among others, previous proposals for automatic blood pressure measuring apparatus have generally involved various types of audio-frequency filtering. Filtering, heretofore, it would appear, has been considered the most effective way to eliminate audio-frequency noise and the effects of noise on the blood pressure measurements.
The above described prior known methods and apparatus as well as others employing low-frequency sound transmitters and receivers, however, are considerably removed from the conventional method of utilizing systolic and Phase IV and V diastolic readings. They are, in contrast to the present invention, concerned principally with sound frequencies as distinguished from sound intensities. It is the latter with which physicians are most familiar and which are employed when taking blood pressures in a conventional manner. Blood pressure readings which are taken using the same criteria -- e.g., sound intensities -- as commonly used by physicians are much more meaningful to a wider number of physicians and consequently more meaningful to the public at large. This is of particular importance because it is to the latter group that the present invention is especially directed.